
==== Front
bioRxiv
BIORXIV
bioRxiv
2692-8205
Cold Spring Harbor Laboratory

10.1101/2024.09.11.612511
preprint
1
Article
Decreased GABA levels during development result in increased connectivity in the larval zebrafish tectum
Liu Yang http://orcid.org/0000-0002-8168-5421

Chen Yongkai http://orcid.org/0000-0003-2800-5949

Duffy Carly R. http://orcid.org/0000-0002-2747-6506

VanLeuven Ariel J http://orcid.org/0000-0002-7725-9534

Byers John Branson http://orcid.org/0000-0003-2404-369X

Schriever Hannah C. http://orcid.org/0000-0002-9459-5548

Ball Rebecca E.
Carpenter Jessica M.
Gunderson Chelsea E. http://orcid.org/0000-0003-0007-7289

Filipov Nikolay M. http://orcid.org/0000-0001-8747-5065

Ma Ping
Kner Peter A. http://orcid.org/0000-0001-7555-5180

Lauderdale James D. http://orcid.org/0000-0001-7503-0528

15 9 2024
2024.09.11.612511https://creativecommons.org/licenses/by-nc-nd/4.0/ This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which allows reusers to copy and distribute the material in any medium or format in unadapted form only, for noncommercial purposes only, and only so long as attribution is given to the creator.
http://biorxiv.org/lookup/doi/10.1101/2024.09.11.612511
nihpp-2024.09.11.612511.pdf
Abstract

γ-aminobutyric acid (GABA) is an abundant neurotransmitter that plays multiple roles in the vertebrate central nervous system (CNS). In the early developing CNS, GABAergic signaling acts to depolarize cells. It mediates several aspects of neural development, including cell proliferation, neuronal migration, neurite growth, and synapse formation, as well as the development of critical periods. Later in CNS development, GABAergic signaling acts in an inhibitory manner when it becomes the predominant inhibitory neurotransmitter in the brain. This behavior switch occurs due to changes in chloride/cation transporter expression. Abnormalities of GABAergic signaling appear to underlie several human neurological conditions, including seizure disorders. However, the impact of reduced GABAergic signaling on brain development has been challenging to study in mammals. Here we take advantage of zebrafish and light sheet imaging to assess the impact of reduced GABAergic signaling on the functional circuitry in the larval zebrafish optic tectum. Zebrafish have three gad genes: two gad1 paralogs known as gad1a and gad1b , and gad2. The gad1b and gad2 genes are expressed in the developing optic tectum. Null mutations in gad1b significantly reduce GABA levels in the brain and increase electrophysiological activity in the optic tectum. Fast light sheet imaging of genetically encoded calcium indicator (GCaMP)-expressing gab1b null larval zebrafish revealed patterns of neural activity that were different than either gad1b-normal larvae or gad1b -normal larvae acutely exposed to pentylenetetrazole (PTZ). These results demonstrate that reduced GABAergic signaling during development increases functional connectivity and concomitantly hyper-synchronization of neuronal networks.

Significance Statement

Understanding the impact of reduced GABAergic signaling on vertebrate brain development and function will help elucidate the etiology of seizure initiation and propagation and other neurological disorders due to the altered formation of neural circuits. Here, we used fast light sheet imaging of larval zebrafish that neuronally expressed a genetically encoded calcium indicator (GCaMP) to assess the impact of reduced GABA levels through null mutation of gad1b during brain development. We show that reduced GABA levels during development result in increased functional connectivity in the brain.
==== Body
pmc
